Problem: $\dfrac{3}{8} - \dfrac{4}{12} = {?}$
Solution: $ = {\dfrac{3 \times 3}{8 \times 3}} - {\dfrac{4 \times 2}{12 \times 2}} $ $ = {\dfrac{9}{24}} - {\dfrac{8}{24}} $ $ = \dfrac{{9} - {8}}{24} $ $ = \dfrac{1}{24}$